A system for image reversion is disclosed in U.S. Pat. No. 5,009,487. There, a prism system is provided for a binocular surgical microscope for image reversion and lateral exchange of two viewing beam paths. The prism system is built up of eight 90° prisms. In each of the 90° prisms, a prism surface, which lies opposite the 90° angle, operates as a mirror. Each viewing beam path is coupled out by such a 90° prism into a plane perpendicular to the optical axis of the microscope lens system in order to be supplied, image reversed, to the other beam path after a two-time reflection. This system of image reversion is mounted in the microscope between the microscope optical tube and a magnification changer. The system can then be switched into and out of the viewing beam path of the surgical microscope.
The text of Neumann-Schröder entitled “Bauelemente der Optik”, Hanser Verlag, Munich (1992), page 174, describes how an image reversion beam path can be made available by multiple reflections at the surfaces of Porro prisms and shortened Porro prisms.
German patent publication 200 21 955 U1 discloses a surgical microscope having an ancillary module which is designed for carrying out surgical procedures in the rear eye section with an ophthalmoscopic magnifier. This ancillary module includes a system for image reversion and is based on a prism construction.
The system is mounted below the surgical microscope main objective and makes an unreversed view of the ocular fundus available to a viewer.
U.S. Pat. No. 5,321,447 discloses a surgical microscope having an ophthalmoscopic ancillary module which is mounted below the microscope main objective as an extension of the microscope tube. This ophthalmoscopic ancillary module has one or several ophthalmoscopic lenses directed toward the objective which function to generate a vertically inverted and laterally inverted image of the ocular fundus of a patient in a first intermediate image plane. The image of this first intermediate image plane is imaged erect and nonreversed into a second intermediate image plane via an optical system for image erection and pupil transposition. The image of this second intermediate image plane can be seen by a microscope viewer through the microscope main objective and a displaceable lens directed toward the microscope main objective. With the ancillary module, the microscope viewer can focus the section of the patient eye which is of interest.
Only a relatively small work space is available to an operator when utilizing such an ophthalmoscopic ancillary module in a surgical microscope. This is so because the ophthalmoscopic lens system has to be mounted closely above the cornea of the eye for imaging the ocular fundus of the eye of the patient. Such ophthalmoscopic ancillary modules are not designed for contact lenses with which the ocular fundus can be made visible in correspondence to an ophthalmoscopic magnifier for which a comparatively large work space is possible for the operator.
The ophthalmoscopic ancillary module, which is described in U.S. Pat. No. 5,321,447, is also not designed for viewing a surgical region by an assistant surgeon with the same quality of viewing as for the primary surgeon. In order to make possible a surgical area companion viewing, the surgical microscope used must be provided with beam coupling units in the region of the microscope tube which split the one viewing beam path into two component beams for the main viewer and the assistant viewer. This configuration, on the one hand, ensures that the main and companion viewers basically see the same image. However, there is a clear brightness loss of the image seen by the main and assistant viewers.
German patent publication 299 05 969 U1 discloses a further stereoscopic surgical microscope wherein ophthalmoscopic magnifiers or contact lenses are used for eye operations for imaging the ocular fundus of a patient eye. This surgical microscope includes an additional lens which can be pivoted into the beam path ahead of the microscope main objective. A system for image reversion which can be pushed in and out is disposed in the microscope optical tube above the magnification changer. This system makes it possible for a surgeon to generate a lateral and pupil correct image of the ocular fundus. This mounting of the system for image reversion has, however, a relatively high microscope assembly as a consequence. This leads to a correspondingly high look-in elevation and a surgeon can only assume an unfavorable work posture. Furthermore, with this construction principle, the microscope image, which is to be seen by a viewer, is not delimited by the size of the microscope main objective but by the dimensioning of the system for image reversion. This has the consequence that a viewer perceives a vignetted or shaded microscope image. Furthermore, if the microscope is, on the one hand, utilized for investigating the ocular fundus of the eye of a patient together with an ophthalmoscopic magnifier or contact glass, and should it then be necessary to remove the ophthalmoscopic magnifier or the contact glass from the beam path for viewing the cornea, then it is necessary to work with changing sharpness adjustments of the microscope. On the one hand, this hinders the surgical sequence and, on the other hand, the focal plane of the optical system is thereby shifted. This last matter has an unwanted magnification change as a consequence for the viewer. Furthermore, with this construction principle it is not possible to correct unwanted imaging errors of additional lenses, ophthalmoscopy magnifiers or contact lenses.
An ancillary module for a stereoscopic surgical microscope is known from German patent publication 3,539,009 wherein the ancillary module includes a system for image reversion and an ophthalmoscopic lens. The system is arranged forward of the microscope main objective. The ocular fundus of the eye is imaged in an intermediate image plane by means of the ophthalmoscopic lens and this intermediate image is located in the ancillary module. The image of this intermediate image plane is projected into the microscope main objective via a field lens and the system for image reversion. Such a microscope configuration causes only a small work space to be provided for an operator and does not make possible a use of contact lenses which are arranged on the eye of the patient. If, during surgery, the ocular fundus of the eye or the vitreous body of the eye of the patient is to be viewed alternately, then the ancillary module has to be removed from the beam path and the focus adjustment of the microscope main objective must be changed.